Throttle pedal weirdness ?

[spudboy6]

  sometimes , probably at least once over a 15 mile / 30 min journey when driving at a steady speed the throttle pedal goes down all by its self causing a sudden acceleration then it comes back up under my foot . It doesn't go to the floor it just dips about 1-2 cm , it could do it several times then not do it for a week , and other days does it all the time .

It's a 1.8 ADZ , I haven't had it on vagcom yet but when it went on last time I did have a stored code for my hall senda .

Any ideas ?

Throttle body and air filter are clean , its had new plugs dizzy cap rotor arm and leads ,

There is a missfire at idle I think not 100% sure as the car vibrates a lot anyways on hockey pucks at the front . But recounter does hunt on idle (800-900) from top of my head .

Replaced vacuum lines on tb and air box , fitted a new rubber gasket on the bottom of the tb.  Now running out of ideas , cars giving back about 60miles to 7.6L (35mpg) so don't think it's effected running ?

Anyways over to you guys !

Thanks for any help

[itavaltalainen]

You must have a gremlin under the bonnet.
I honestly cannot see why the pedal would be moving by itself, it's just a steel cable going from the throttle pedal to the throttle body.... Does it physically move or does the car just accelerate by itself? not sure i'd have the guts to look at the pedal if my gremlin started accelerating tbh

When you last checked fault codes wrt to hall sender.... was the engine running or not? I suspect not, as IF your hall sender was actually broken your 1.8 engine wouldn't be running at all!

how is the engine running otherwise? smooth idle?
Have a look at the flange between inlet manifold and mono motronic fuel injection unit. if cracked and sucking in air replace...

[Jasikasisback]

my car has been doing this since i bought it and does it from time to time. mine runs rich and i believe that is the key but don't know how to fix it. almost stalls out sometimes as well on startup. i also have no idea as to why but possibly ecu corecting fuel/air ratio by adjusting throttle on deacceleration? just my guess. i tood my friend who is a mechanic and he didn't believe me. but you are not the only one. should get together and compare cars:)

[spudboy6]

You must have a gremlin under the bonnet.
I honestly cannot see why the pedal would be moving by itself, it's just a steel cable going from the throttle pedal to the throttle body.... Does it physically move or does the car just accelerate by itself? not sure i'd have the guts to look at the pedal if my gremlin started accelerating tbh

When you last checked fault codes wrt to hall sender.... was the engine running or not? I suspect not, as IF your hall sender was actually broken your 1.8 engine wouldn't be running at all!

how is the engine running otherwise? smooth idle?
Have a look at the flange between inlet manifold and mono motronic fuel injection unit. if cracked and sucking in air replace...

The pedal physically moves and the car briefly accelerates then the pedal comes back ! , I've changed that flange on the injection unit , the hall senda fault came up when car was on vagcom ignition second position not running .

My idle hunts sometimes but hard to tell as the engine is on hockey pucks so lots of vibrations but the needle does indicate a missfire .

[spudboy6]

my car has been doing this since i bought it and does it from time to time. mine runs rich and i believe that is the key but don't know how to fix it. almost stalls out sometimes as well on startup. i also have no idea as to why but possibly ecu corecting fuel/air ratio by adjusting throttle on deacceleration? just my guess. i tood my friend who is a mechanic and he didn't believe me. but you are not the only one. should get together and compare cars:)

It's not ideal is it ? Just plain weird and I can't work it out or see how its doing it !

Is yours a 1.8 ? How many miles does it do on £10 ?

[itavaltalainen]

@Jasikasisback It would key to know which engine you've got. Ideally engine letters (on cambelt cover, service book or configuration tag in boot)....

@spudboy6 - When does it accelerate by itself? is the pedal assy solid, bushes and pin not worn?
Did you have a look @ TB?

[spudboy6]

@Jasikasisback It would key to know which engine you've got. Ideally engine letters (on cambelt cover, service book or configuration tag in boot)....

@spudboy6 - When does it accelerate by itself? is the pedal assy solid, bushes and pin not worn?
Did you have a look @ TB?

It does it on steady throttle say at 50mph with foot just resting on the pedal . Then it goes down on its own , then comes back up under my foot and car judders almost like stalling  .

Throttle body is clean and free , bushes all look and feel tight ,

[itavaltalainen]

Does the throttle go back smoothly when you pull the cable/lever manually at the throttle body, does it judder?

If not then either cable or there is such a massive vacuum that is pulling the throttle open. That should not be the case if the idle gap is clean.... Far shot: is the breather pipe clear?

[VW BUSH]

Does it not have a motorised Throttle body?

[spudboy6]

Does it not have a motorised Throttle body?

Iirc there is a plug In to the throttle body ,

Will have a pull on the cable later but feels smooth when operating pedal by hand .